Bandpass Outputs Research Articles

Cladding-mode extraction from long-period fibre grating using self-aligned core-mode blocker

A novel method is presented of fabricating a core-mode blocker for use in long-period fibre gratings by forming a self-aligned absorber on the end of the fibre core. The absorber efficiently suppresses the core-mode power and allows the cladding-mode radiation to pass through, thereby resulting in a bandpass output at the resonant wavelengths.

Tunable optical narrowband filter using a gain-coupled phase-shift-controlled distributed feedback laser

In this paper, we have proposed and analyzed a new tunable optical narrowband filter using gain-coupled phase-shift-controlled distributed feedback (GC-PSC-DFB) laser diode. Coupled-mode equations are solved by using the transfer matrix method (TMM). The GC-PSC-DFB filters offer a stable single-mode bandpass output, similar to that obtained with phase-shifted index-coupled structures. However, GC structures do not suffer from the severe longitudinal spatial hole burning (SHB) that occurs in high-coupling quarter-wave-shifted DFB filters. This SHB can cause multimoded behavior for high-input signal power. Various filter parameters such as wavelength tuning range, side-mode suppression ratio (SMSR), and channel gain deviation have been investigated and discussed. Our results show that the GC DFB structures offer a wider tuning range of 23.3 /spl Aring/ compared with the similar index-coupled DFB structures with nearly steady bandwidth of 12 GHz, while maintaining 41.8-dB constant gain.

An efficient computational scheme for the two-dimensional overcomplete wavelet transform

We have studied the computational complexity associated with the overcomplete wavelet transform for the commonly used spline wavelet family. By deriving general expressions for the computational complexity using the conventional filtering implementation, we show that the inverse transform is significantly more costly in computation than the forward transform. To reduce this computational complexity, we propose a new spatial implementation based on the exploitation of the correlation between the lowpass and the bandpass outputs that is inherent in the overcomplete representation. Both theoretical studies and experimental findings show that the proposed spatial implementation can greatly simplify the computations associated with the inverse transform. In particular, the complexity of the inverse transform using the proposed implementation can be reduced to slightly less than that of the forward transform using the conventional filtering implementation. We also demonstrate that the proposed scheme allows the use of an arbitrary boundary extension method while maintaining the ease of the inverse transform.

Fast algorithm for over-complete wavelets

The computational complexity of the over-complete wavelet representation is studied. It is found that the inverse transform is nearly three times more costly in computation than the forward transform. By exploiting the redundancy between the lowpass and the bandpass outputs, the computation is greatly simplified, resulting in an efficient inverse.

Low power current-mode second-order bandpass IF filter

A controlled active inductance implemented from two current-controlled conveyors in conjunction with one capacitor is introduced. Calculation, taking all the parasitics of the conveyors into account, shows that with this design the phase deviation from ideal is pushed up to very high frequency. A second order bandpass filter operating in current-mode has been implemented from this controlled inductance. This filter exhibits two bandpass outputs. One has unity gain and the other, which can be used for Q-tuning purpose, has a magnitude-gain at f/sub 0/ directly proportional to the Q-factor. An integrated circuit prototype of an IF receiver stage for the GSM cellular telephone has been designed from two cascaded identical second-order bandpass cells above. This circuit, which is intended to replace a surface acoustic wave (SAW) filter, was centered at 85 MHz. Simulation and measurement results are given for this prototype. They show interesting performances in conjunction with very low power consumption: less than 38 mW for the entire IF stage under /spl plusmn/2.5 V supply.

A CMOS programmable balanced output transconductor for analogue signal processing

A new CMOS programmable balanced output transconductor (BOTA) is introduced. The BOTA is a useful block for continuous-time analogue signal processing. A new CMOS realization of the BOTA is given. The proposed realization is based on the cascaded connection of a new voltage controlled differential transconductor, a voltage controlled MOS grounded resistor and a balanced output transconductor stage. Applications of the BOTA in realizing a floating resistor, a balanced output differential integrator, a continuous-time balanced output bandpass–lowpass filter, a floating inductor and the active realization of the RLC filters using a minimum number of the BOTA are given. PSpice simulation results for the BOTA circuit and for its applications are also given.

L-band integrated feed array design for mobile communication satellites

The space segment of a mobile communication satellite system such as the North American Mobile Communication Satellite System (MSAT) must provide high radiated power densities on the ground to allow mobiles with small, low-gain antennas to communicate via satellite. With the emerging high-power mobile communication satellite systems, the risk of interference caused by passive intermodulation (PIM) is a very important spacecraft design performance parameter. Separate transmit and receive reflector antennas are used on the MSAT spacecraft to reduce the risk of PIM. In addition, PIM avoidance is a major design driver for the transmit antenna reflector and primary feed array. Significant design effort and breadboard activities at Spar have resulted in the development of a primary feed array suitable for mobile satellite applications. The authors present the integrated feed design approach which has been selected. The author describes the feed element, which consists of an output band-pass filter integrated with a cup dipole radiator. The measured test results of the developed hardware are also presented.

TOCA-based electronically-tunable continuous-time filters

Abstract A new CMOS translinear operational current amplifier (TOCA) and continuous-time ladder filters using the proposed TOCAs are presented. The TOCA based integrators provide better high frequency properties and require less capacitance compared with their counterparts which use conventional operational amplifiers. A sixth-order band-pass ladder filter with centre frequency 455 kHz, 0-5 dB ripple, and 80kHz bandwidth is simulated. A third-order electronically tunable low-pass ladder filter with 0-3 dB ripple and a biquad filter with low-pass and band-pass outputs are experimentally demonstrated using TOCAs which are realized with discrete components. The techniques will be useful for monolithic integration in the analogue filtering circuits.

A switched capacitor biquad filter

This paper reports the realization of a switched capacitor biquad filter using discrete components. This filter is one type of biquad which gives lowpass, highpass, bandpass and notch outputs. This circuit was fabricated using CMOS switches and μA741 operational amplifiers. The experimental results and computer simulation using the SWITCAP program were compared. The agreement was found to be satisfactory.

A Simple, Approximate Method of Generating Baseband-Serial MSK

An alternate derivation of the serial formulation of the MSK signal leads to an approximate implementation that is based on filtering an easily generated three-level data signal through a high- <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</tex> , two-pole filter whose low-pass and bandpass outputs are modulated onto quadrature carriers.

System for maximum efficient transfer of modulated audio frequency energy

An audio processing system for maximizing the efficiency of transferring audio frequency signals. Signals to be processed are supplied to a bandpass input filter, then to a primary active frequency control. Its output drives a primary voltage compressor selectively limiting audio dynamics to a predetermined window, the latter being controllably preset and driven with different audio bands of amplitude determined by the primary frequency control to maximum compression levels indicated by a visual indicator. The output of the primary compressor is presented to a secondary active frequency control driving a secondary dynamic compressor with different audio bands. A second visual indicator indicates maximum compression levels of the latter. An automatic gain control (AGC) tied to the secondary compressor supplies feedback to the primary voltage compressor via AGC circuitry to control primary compression as a function of average, overall dynamic compression of the system. The AGC circuitry also feeds a third visual indicator which displays average compressed output voltage. The processed output of the secondary compressor is provided to a bandpass output filter and, sharply frequency attenuated by the latter, is delivered for further use. A high level output stage is also selectively utilized for driving auxiliary devices.

Hyperoptic translator system

A sound-to-optic translator system for the hard-of-hearing is disclosed. Light-emitting diodes of different colors provide sources of light that are hyperoptically (out-of-focus) located directly in front of the pupil of the eye and along the normal line-of-sight to project overlapping color discs onto the macula area of the retina to be sensed by the cones. The diodes are supported by a T member having a width approximately one-half or less than the diameter of the pupil under normal reading light intensity and positioned at less than distance of focus of the eye. Audio frequencies are separated into a plurality of bands by bandpass filters and outputs of the respective filters drive respective diodes to hyperoptically transmit colors onto the macula.

Comments on "A low-pass biquad derived filter realization"

In the above paper, Brodie (see ibid., vol.SC-11, p.552-5, 1976) presents a biquad low-pass filter which requires only two operational amplifiers. The use of current differencing amplifiers for reduced operational amplifier count implementation of the biquad filter has been around for some time. However, Brodie does not mention that the low-pass form is not the only filter that can be achieved. If one allows one additional resistor for biasing, a true bandpass output is available.

A multiple-feedback universal active filter

This paper presents a basic active-RC network synthesis technique that results in the implementation of a second-order universal filter providing simultaneously low-pass, bandpass and high-pass output responses. The proposed technique, based on multiple-feedback concepts, simulates a passive R-L-C bandpass prototype under ideal operational-amplifier conditions. Finite operational-amplifier open-loop gain and bandwidth effects arc subsequently investigated through the introduction of parasitic elements to the idealized model. Results provided by this rather intuitive approach arc shown to be in excellent agreement with those of more sophisticated computer-analysis methods. Advantages of the basic technique include versatility, modularity, canonicitiy, low element spreads, low-impedance outputs, low active and passive ω0 and Q sensitivities, ease of tuning, and the capability of generating biquadratie functions for the realization of higher-order filter configurations.

Signal-to-Noise Ratio in the Bandpass Output of a Discriminator

A formula is derived for the output signal-to-noise power ratio from a limiter-discriminator that is followed by an ideal (rectangular) bandpass filter. This signal-to-noise ratio is shown to be inversely proportional to the difference between the cube of the upper cutoff frequency and the cube of the lower cutoff frequency. The formula commonly utilized by designers for the discriminator output signal-to-noise ratio was derived for the case of a lowpass filter on the discriminator output. The bandpass and low-pass formulas are compared to indicate 1) the advantage of bandpass filtering for the discriminator output, and 2) the error incurred if the designer employs the low-pass formula to evaluate the performance of a bandpass filter design. Finally, the accuracy of a narrow-band approximation for the bandpass formula is evaluated.

Sensitivity of optical data processing to changes in rock fabric. Part I—Geometric patterns

Idealized geometric patterns have been used as input test data to determine the sensitivity of optical data processing to changes in fabric. Useful test results have been obtained for separating input components of different directions or different spatial frequencies, measuring elongation of simulated grains and determining their stacking geometry, and filtering for band-pass and high-cut outputs. All of the operations performed here and the results ontained are directly transferable to rock fabric inputs.

Ring Network Filter (Correspondence)

A filter circuit comprising two ring networks which are connected by two quarter-wavelength lines is described. This circuit has one output with a relatively wide pass band and a second output with a sharp rejection band. A printed microstrip version designed for 1-Gc operation is shown in Fig. 1. Input is at terminal 1, band-pass output at terminal 3, and rejection band output at terminal 2.